Materials which are used for electric current carrying components constituting electrical or electronic components such as connectors, lead frames, relays, and switches are required to have high “strength” capable of withstanding a stress which is given at the time of assembling or operation of an electrical or electronic appliance. In addition, materials used for electrical or electronic components are required to have excellent “bending workability” because said components are generally formed by bending. Furthermore, in order to ensure contact reliability between electrical or electronic components, durability against a phenomenon in which a contact pressure decreases with time (stress relaxation), namely excellent “stress relaxation resistance” is required, too. The stress relaxation as referred to herein is a kind of creep phenomenon in which even if the contact pressure of a spring part of an electric current carrying component constituting an electrical or electronic component is kept in a fixed state at ordinary temperature, it decreases with time under an environment of relatively high temperatures (for example, from 100 to 200° C.). That is, the stress relaxation means a phenomenon in which in a state where a stress is given to a metal material, dislocation moves due to self-diffusion of atoms constituting the matrix or diffusion of a solute atom to cause plastic deformation, whereby the given stress is relieved. When used in an environment where an increase of the component temperature as in automobile connectors is supposed, the “stress relaxation resistance” is particularly important.
In the light of the above, materials which are used for electrical or electronic components are required to have excellent “strength”, “bending workability”, and “stress relaxation resistance”. Meanwhile, electric current carrying components having a movable portion, such as relays and switches, are also required to have excellent “fatigue resistance” in terms of durability capable of withstanding a repeated stress load. But, in general, the “fatigue resistance” or “bending workability” is in a trade-off relationship with the “strength”, and in copper alloy sheet materials, it is not easy to enhance the “fatigue resistance” or “bending workability” at the same time while contemplating to achieve high strength.
Among copper alloys, a Cu—Ti based copper alloy has high strength just below a Cu—Be based copper alloy and has stress relaxation resistance superior to the Cu—Be copper alloy. In addition, the Cu—Ti based copper alloy is more advantageous than the Cu—Be copper alloy from the standpoints of cost and environmental load. For that reason, the Cu—Ti based copper alloy (for example, C1990 which is a Cu-3.2% by mass Ti alloy) is used for connector materials or the like as an alternate material of the Cu—Be based copper alloy. But, the Cu—Ti based copper alloy is generally inferior in the “fatigue resistance” and “bending workability” to the Cu—Be copper alloy having equal strength.